Over 100 survivors had so far been pulled out by rescuers from the rubble of Rajpoot Polyester polythene bag factory which collapsed in the Sundar Industrial Estate area on Wednesday during its expansion work.
A rescue official said the search and rescue operation went on non-stop as part of efforts to find survivors still trapped.
"31 bodies have now been recovered by rescue crews using heavy construction machinery and other tools to dig through the debris, rescue official was quoted as saying by Geo TV.
It was unclear how many people were in the building when it collapsed or how many - dead or alive - may still be trapped, but officials have said at least 150 people were in the factory when it came down, rescue official said.
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Noting that the focus of the operation was on the search for survivors, a top administration official said that over 100 people had been rescued.
He said rescuers were using audio and video technology during the search operation.
Injured survivors said Ashraf, who was adding a new floor to the building, had ignored advice from his contractor and pleas from his workers to stop construction after cracks in the walls following a powerful earthquake on October 26.
Army was also called in during the night as officials scrambled to clear the site. The army said specialists were deployed at the spot to help the rescue effort.
Soldiers and rescuers were busy lifting the debris of the collapsed-structure, less than two weeks after a 7.5-magnitude earthquake jolted the nation, killing nearly 400 people across Pakistan and Afghanistan.